Inverse obstacle problem for the non-stationary wave equation with an unknown background

We consider boundary measurements for the wave equation on a bounded domain $M \subset \R^2$ or on a compact Riemannian surface, and introduce a method to locate a discontinuity in the wave speed. Assuming that the wave speed consist of an inclusion in a known smooth background, the method can determine the distance from any boundary point to the inclusion. In the case of a known constant background wave speed, the method reconstructs a set contained in the convex hull of the inclusion and containing the inclusion. Even if the background wave speed is unknown, the method can reconstruct the distance from each boundary point to the inclusion assuming that the Riemannian metric tensor determined by the wave speed gives simple geometry in $M$. The method is based on reconstruction of volumes of domains of influence by solving a sequence of linear equations. For \tau \in C(\p M) the domain of influence $M(\tau)$ is the set of those points on the manifold from which the distance to some boundary point $x$ is less than $\tau(x)$.Comment: 4 figure

Environment-induced mixing processes in quantum walks

The mixing process of discrete-time quantum walks on one-dimensional lattices is revisited in a setting where the walker is coupled to an environment, and the time evolution of the walker and the environment is unitary. The mixing process is found to be incomplete, in the sense that the walker does not approach the maximally mixed state indefinitely, but the distance to the maximally mixed state saturates to some finite value depending on the size of the environment. The quantum speedup of mixing time is investigated numerically as the size of the environment decreases from infinity to a finite value. The mixing process in this unitary setting can be explained by interpreting it as an equilibration process in a closed quantum system, where subsystems can exhibit equilibration even when the entropy of the total system remains zero.Comment: 11 pages. Same as the published versio

High Clear Bell of Morning by Ann Eriksson

Review of Ann Eriksson\u27s High Clear Bell of Morning

Where Rhetoric and Lean Meet

This paper aims at an initial analysis and explanation of lean through the lens of the discipline of rhetoric. First, the ancient origin, central ideas, subsequent history and current interpretations of rhetoric are outlined. Then, the overall meeting points of rhetoric and lean are discussed. At the outset, it is contended that certain arguments that can be used as a justification in rhetoric seem fertile for understanding the difference between lean and conventional management. Then, persuasion towards compliance in production is discussed. The field of visual management is argued to have an implicit foundation in rhetoric. The existence of a common ground of values, facts and presumptions between the speaker and the audience is emphasized in rhetoric; it is contended that lean construction in many ways endeavours to create such a common ground among the project participants. Regarding deliberation, the rhetorical dimensions in the methods of A3 and Choosing by Advantages are discussed. Further, Target Value Design is identified as based, for their part, on rhetorical ideas. In conclusion, it is contended that many aspects of lean, which as such may seem odd and perhaps peri